Figure 1. Virulence factors of Pseudomonas aeruginosa. P. aeruginosa has both cell-associated (flagellum, pilus, nonpilus adhesins, alginate/biofilm, lipopolysaccharide [LPS]) and extracellular virulence factors (proteases, hemolysins, exotoxin A, exoenzyme S, pyocyanin).

Figure 3. Cell-to-cell signaling systems. Cell-to-cell signaling systems are composed of two genes. The I gene encodes an autoinducer synthase and the R gene encodes a transcriptional activator protein (R-protein). The autoinducer synthase is responsible for the synthesis of an autoinducer molecule (AI), which crosses the cell membrane. With increasing cell-density the intracellular concentration of AI reaches a threshold level, and the AI then binds to the transcriptional activator. The complex R-protein/AI activates the expression of specific target genes.

Figure 4. The cell-to-cell signaling circuitry of P. aeruginosa. The las cell-to-cell signaling system controls the rhl cell-to-cell signaling system in a hierarchy cascade. The LasR/3- oxo- C12-HSL complex activates the transcription of rhlR, and 3-oxo-C12- HSL blocks the activation of RhlR by C4-HSL. The las system itself is controlled positively by Vfr and GacA, and negatively by RsaL. 3-oxo-C12- HSL is required for biofilm differentia- tion and has immunomodulatory activity. Both cell-to-cell signaling systems regulate the expression of numerous genes (lasB: LasB elastase, lasA: LasA elastase, toxA: exotoxin A, aprA: alkaline protease, xcpP and xcpR: genes of the xcp secretory pathway, rhlAB: rhamnosyltransferase required for rhamnolipid production, rpoS: stationary phase sigma factor).